1. Field of the Invention
This invention relates generally to the melting of scrap metal, and more particularly, to a method and apparatus for preheating scrap metal in a double-hearth arc furnace, especially for the production of steel.
2. Description of the Prior Art
In steel production, it is desirable to preheat charge material, such as scrap metal for example, before they are inserted into the furnace. In an electric arc furnace, this is typically accomplished by utilizing a feed line to deliver hot waste gases of the furnace into contact with scrap material disposed in a cage or basket. After the heat of the waste gas has been advantageously utilized in this manner, it is subsequently supplied to a gas purification station for treatment and subsequent release into the atmosphere.
Another conventional technique for preheating the scrap material is to arrange two arc furnaces next to one another and to fill one furnace, which is in the process of preparing molten material, with scrap beforehand and thereby use the furnace as a preheating chamber. In U.S. Pat. No. 4,531,971, for example, there is disclosed a double furnace installation in which a first of the two furnaces is supplied with electric current in order to melt the charge contained therein and the second furnace is completely isolated from the main power supply. The isolated second furnace is charged with scrap and vessel cover thereof is closed. Subsequently, the flue gas generated by the first or operating furnace is withdrawn by vacuum and introduced into the isolated furnace via a connection line provided between the two furnaces.
In accordance with the process disclosed in the aforementioned patent, the flue gas is sucked out of the operating furnace via the laterally disposed cover thereof and is blown onto the scrap from the direction of its laterally disposed cover. As a result, only a portion of the scrap is exposed to the heated gas, and, consequently, only a portion of the sensible heat of the flue gas is taken up by this scrap.
Accordingly, it is an object of the present invention to avoid the disadvantages mentioned above and to provide, with the use of simply designed structural component parts, a low-maintenance and highly reliable steel making plant with a double furnace arrangement.
It is another object of the present invention to provide a process and apparatus for preheating scrap in a double hearth furnace installation in which the flue gas is transported from the operating furnace to the isolated furnace through easily maintained lines and in which the flue gas is brought into intimate contact with the scrap while avoiding the cold zones.